The present invention pertains, in general, to a process for producing aromatic hydrocarbon compounds of liquid phase and non-aromatic hydrocarbon compounds of gas phase, for instance, liquefied petroleum gas (LPG), from hydrocarbon feedstock, and a catalyst useful therefor. More specifically, the present invention pertains to a process for converting aromatic compounds in hydrocarbon feedstock having boiling points of 30-250xc2x0 C. to oil components including BTX (benzene, toluene and xylene) through dealkylation and/or transalkylation, and for converting non-aromatic compounds to LPG-rich gaseous components through hydrocracking; and a catalyst used in said process.
Generally, aromatic hydrocarbons are separated from non-aromatic hydrocarbons by subjecting feedstocks abundantly containing aromatic compounds, such as reformate produced through a reforming process and pyrolysis gasoline obtained from a naphtha cracking process, to solvent extraction. The aromatic hydrocarbons obtained as above is separated as benzene, toluene, xylene, and C9 or higher aromatic compounds, according to their different boiling points, and thus used as fundamental materials of the petrochemical industry. Non-aromatic hydrocarbons are used as raw materials or fuel of the naphtha cracking process.
In this regard, U.S. Pat. No. 4,058,454 refers to a solvent extraction process for separating and recovering polar hydrocarbons from hydrocarbon mixture including polar hydrocarbons and non-polar hydrocarbons. Such solvent extraction process uses polarity of aromatic hydrocarbons to achieve separation. That is, when polar materials-dissolving solvents, such as sulfolane, are contacted with hydrocarbon mixture, polar aromatic hydrocarbons can be selectively dissolved and thus separated from non-polar non-aromatic hydrocarbons. Said process is advantageous in terms of obtaining high purity aromatic hydrocarbon mixture, while is disadvantageous in requiring additional solvent-extraction equipments and continuously feeding solvents during operation of equipment. Therefore, the methods for separating aromatic hydrocarbons and non-aromatic hydrocarbons from raw oils without additional solvent extraction process have been devised.
In particular, much research into reaction systems, instead of solvent extraction processes, for separating aromatic compounds from non-aromatic compounds, has been carried out. Non-aromatic compounds mixed with aromatic compounds are converted to gaseous hydrocarbons in the presence of a catalyst through hydrocracking, and aromatic compounds can be separated from non-aromatic compounds using a gas-liquid separator at the rear end of a reactor. Such concept has been advanced from U.S. Pat. No. 3,729,409. In addition, U.S. Pat. Nos. 3,849,290 and 3,950,241 refer to a method for producing volatile oil components of good quality by converting linear hydrocarbon components mixed with aromatic compounds to gaseous components in the presence of ZSM-5 typed zeolite through hydrocracking, thus increasing the content of aromatics in liquid components. A more developed concept, U.S. Pat. No. 5,865,986 discloses a process for upgrading a petroleum naphtha fraction, in which the production of benzene/toluene is increased by filling zeolite-based catalyst in the parts of a series of reactors during upgrading processes. Also, U.S. Pat. No. 6,001,241 refers to a method for increasing the yield of aromatic compounds by filling zeolite-based catalyst in the parts of reactors during upgrading processes. However, nowhere are found processes taking advantage of such concept as an independent process from reforming reactors aiming exclusively to the production of aromatic compounds. By the process independent from such a reforming reactor, liquefied petroleum gas can be produced, along with aromatic compounds, through the treatment of raw oils such as reformate and pyrolysis gasoline. In countries such as Korea, importing most of liquefied petroleum gas (LPG), considerable amounts of imported energy may be replaced with liquefied petroleum gas produced as by-products of the reaction.
However, said techniques have many limitations to their commercial use. In particular, the sedimentation of coke on the catalyst causes a side reaction, thus shortening the life span of the catalyst. Hence, techniques for overcoming this problem are required. The sedimentation of coke can be restrained by supporting metal components with high hydrogenation activity, such as metals of group VIII in the periodic table, onto zeolite. However, strong hydrogenation activity attributed to such metal components causes another side reaction of converting aromatic compounds to naphthenic compounds through hydrogenation. Therefore, such hydrogenation function by metal components needs to be controlled. Said U.S. Pat. No. 5,865,986 refers to controlling metal activity by use of sulfur compounds. Additionally, in U.S. Pat. No. 6,001,241, the degree of hydrogenation is controlled using lead or bismuth. Under these circumstances, research for controlling hydrogenation activity of VIII group metals by introducing second metal components has been carried out.
Leading to the present invention, the intensive and thorough research on production of aromatic hydrocarbons and liquefied petroleum gas, carried out by the present inventors aiming to avoid the problems encountered in the prior arts, resulted in the finding that a hydrocarbon feedstock such as reformate, pyrolysis gasoline and the like can be converted to aromatic hydrocarbon compounds of liquid phase and gaseous non-aromatic hydrocarbon compounds in the presence of tin-platinum or lead-platinum supported zeolite-based catalyst, without additional solvent extraction process, thus obtaining aromatic hydrocarbon mixture of high purity and LPG as by-product.
Therefore, it is an object of the present invention to provide a process for producing aromatic hydrocarbons of high purity and liquefied petroleum gas (LPG) as by-product from a hydrocarbon feedstock without solvent extraction.
It is another object of the present invention to provide a process for upgrading aromatic hydrocarbons in a hydrocarbon feedstock such as reformate, pyrolysis gasoline and the like.
It is further object of the present invention to provide a process for converting non-aromatic hydrocarbon components in a hydrocarbon feedstock to LPG-enriched gaseous products in the presence of a catalyst through hydrocracking.
It is still another object of the present invention to provide a zeolite-based catalyst, suitable for use in said process.
In accordance with the present invention, the process for producing aromatic hydrocarbon compounds and liquefied petroleum gas (LPG) from a hydrocarbon feedstock, comprising the following steps of:
a) introducing hydrogen and a hydrocarbon feedstock with boiling points of 30-250xc2x0 C. to at least one reaction zone;
b) converting the hydrocarbon feedstock in the presence of the catalyst to aromatic hydrocarbon compounds which are abundant in benzene, toluene and xylene (BTX) through hydrodealkylation and/or transalkylation, and to non-aromatic hydrocarbon compounds which are abundant in LPG through hydrocracking within the reaction zone; and
c) recovering the aromatic hydrocarbon compounds and LPG, respectively from the resulting products of said step b), through gas-liquid separation and distillation;
wherein said catalyst comprises platinum/tin or platinum/lead and a mixture support consisting of 10-95 wt % of zeolite having a molar ratio of silica/alumina of 200 or less and 5-90 wt % of inorganic binder, said zeolite being selected from the group consisting of mordenite, beta type zeolite, ZSM-5 type zeolite and a mixture thereof, in which said platinum is present at an amount of 0.01-0.5 parts by weight, and said tin is present at an amount of 0.01-5.0 parts by weight or said lead is present at an amount of 0.02-5.0 parts, on the basis of 100 parts by weight of said mixture support.